Experimental and numerical analysis of nitric oxide effect on the ignition of iso-octane in a single cylinder HCCI engine

Abstract

Small concentrations of very reactive chemical species such as nitric oxide (NO) have a very important impact on the onset of combustion. In engine applications, this may lead to irregular combustion phenomena in spark ignition engines or contribute to the control of the homogeneous charge compression ignition (HCCI) engines. To numerically analyze and predict the effect of these species, detailed chemical mechanisms are required. However, including these mechanisms in computational fluid dynamics (CFD) simulations often results in prohibitive computational cost. Using a single-cylinder HCCI engine test bench, we have analysed the effect of initial NO concentrations ranging from 0 to 500ppm on the ignition of iso-octane. We have also investigated whether the tabulation of dynamic adaptive chemistry (TDAC) method, that significantly reduces the CPU time associated with using detailed chemistry in CFD simulations, could capture this effect. This paper first presents the experimental setup and the validation data. Then it compares these experimental data with the CFD simulation results using a detailed mechanism involving more than 1000 species and 4500 reactions. The significant effect of NO on iso-octane ignition is efficiently captured over the whole range of NO concentration with a speed-up factor of up to 1500 (compared to simulations without TDAC). This work further demonstrates that TDAC represents a very efficient tool to include detailed kinetic mechanisms able to describe complex phenomena, such as the kinetic effect of small concentrations of reactive species, on ignition in a HCCI engine.